Evaluation of the Landsat-8 Albedo Product across the Circumpolar Domain

Round 1

Reviewer 1 Report

Review of Evaluation of the Landsat Circumpolar Albedo Products by Erb et al.

The manuscript aims to develop and validate surface albedo product from 40 °N to 84 °N from Landsat-8 satellite. This is a much-needed dataset and hope soon it will be translated into an operational Landsat global albedo product. The manuscript is well written and easy to follow. In my opinion, the manuscript is suitable for publication after incorporating the changes given below.

I would suggest the authors to expand the methodology section lines 95-108 and explain how the information provided in the references therein [23-29] are used in this work? The reader of this manuscript may not have access to all the cited literature here and may miss out on important aspects. Hence, please add all the necessary and relevant equations, assumptions and input data used to generate this dataset from references 23-29 cited here. I believe that this paper must be self-supporting as it discusses the generation of a new dataset.

Lines 122-123 MODIS may not view the ground from NADIR view angle always. Hence, how the reflectance obtained from MODIS can be combined with the albedo product to generate the A/N ratio? Have you used NABR product from MODIS? Please clarify.

Line 180: the word scattering is mis-spelt.

In Figure 2, I can see a SW white sky albedo map. In addition to spectral albedo in each band, due to also provide visible (0.4-0.7 µm) and shortwave (0.4 to 3 µm) albedo products from Landsat? If yes, how SW albedo is created from spectral albedo?

Author Response

Dear reviewer,

 

Thank you for spending so much time reviewing this work and for your thoughtful and considered comments.  We have done our best to address the issues highlighted.   We appreciate your help in this process and do believe that our manuscript has been improved because of your comments.  Please see our responses below.

Reviewer 1:

Review of Evaluation of the Landsat Circumpolar Albedo Products by Erb et al.

The manuscript aims to develop and validate surface albedo product from 40 °N to 84 °N from Landsat-8 satellite. This is a much-needed dataset and hope soon it will be translated into an operational Landsat global albedo product. The manuscript is well written and easy to follow. In my opinion, the manuscript is suitable for publication after incorporating the changes given below.

I would suggest the authors to expand the methodology section lines 95-108 and explain how the information provided in the references therein [23-29] are used in this work? The reader of this manuscript may not have access to all the cited literature here and may miss out on important aspects. Hence, please add all the necessary and relevant equations, assumptions and input data used to generate this dataset from references 23-29 cited here. I believe that this paper must be self-supporting as it discusses the generation of a new dataset.

I do appreciate that this paper should be self-supporting, however, much of this information is explained in the following paragraphs, I have added reference to the further explanation in the first paragraph. I have also made specific data products used clearer and expanded the methods section including the information on the representativeness assessment. The MODIS albedo and Landsat surface reflectance are standard products, this Landsat product will be delivered to the LPDAAC this year.

Lines 122-123 MODIS may not view the ground from NADIR view angle always. Hence, how the reflectance obtained from MODIS can be combined with the albedo product to generate the A/N ratio? Have you used NABR product from MODIS? Please clarify.

True, to generate the AN ratio we use MCD43 products to calculate the albedo and reflectance at the near nadir geometry of the Landsat satellite. These are then used for the AN ratio; this is clarified in line 165.

Line 180: the word scattering is mis-spelt.

Thank you, this has been corrected

In Figure 2, I can see a SW white sky albedo map. In addition to spectral albedo in each band, due to also provide visible (0.4-0.7 µm) and shortwave (0.4 to 3 µm) albedo products from Landsat? If yes, how SW albedo is created from spectral albedo?

Thank you, the product includes individual bands from Landsat 8, 2-7, NIR, VIS and SW bands using the narrow to broad band coefficients presented in Wang et. al.  This has been clarified at the end of the methods section.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper presents land surface albedo at 30m resolution at  high latitudes  across diverse land cover and conditions, derived from  the Landsat satellite system  coupled with BRDF  from the MODIS. The product is extensively validated and performs well  when compared to coincident tower data.

The results are of interests to the community, and the paper is well organized.  Recommend it for publication at its present form. 

Comments for author File: Comments.pdf

Author Response

 

Dear reviewer,

 

Thank you for your support and positive impressions of our manuscript.   We appreciate you taking the time to review it.

 

Reviewer 2:

This paper presents land surface albedo at 30m resolution at high latitudes across diverse land cover and conditions, derived from  the Landsat satellite system  coupled with BRDF  from the MODIS. The product is extensively validated and performs well when compared to coincident tower data.

The results are of interests to the community, and the paper is well organized.  Recommend it for publication at its present form. 

Thank you for your review and consideration, we appreciate your time.

 

Author Response File: Author Response.docx

Reviewer 3 Report

In this manuscript the authors present the further development and evaluation of a 30m Landsat albedo product, including an operational blue-sky albedo product, for application in the northern latitudes. The manuscript is well written and in addition to providing the most important references on the subject it is also novel. I suggest that the manuscript be accepted in its current format. 

Author Response

 

Dear reviewer,

 

Thank you for your support and positive impressions of our manuscript.   We appreciate you taking the time to review it.

 

Reviewer 3:

In this manuscript the authors present the further development and evaluation of a 30m Landsat albedo product, including an operational blue-sky albedo product, for application in the northern latitudes. The manuscript is well written and in addition to providing the most important references on the subject it is also novel. I suggest that the manuscript be accepted in its current format. 

Thank you for your review and consideration, we appreciate your time.

 

 

Author Response File: Author Response.docx

Reviewer 4 Report

The manuscript is devoted to the development and evaluation of a specific Landsat albedo product. Generally, the research satisfies the requirements for publications however, the authors need to consider the following questions.

 

1. The title is too broad and confusing

2.  The section materials and methods are not concentrated on the exact methods and data that have been used.

3. Fig 1 is too small, no idea that it could be obtained from that map. 

4. Table 1 is too long and can be sent in the appendix. 

 

This research needs to clarify the situation with permafrost that covers a major part of the region and has big uncertainties with a contribution to albedo. I found only "Tundra Vegetation".  What about other types of permafrost? 

Author Response

Dear reviewer,

 

Thank you for spending so much time reviewing this work and for your thoughtful and considered comments.  We have done our best to address the issues you have highlighted in your response.   We appreciate your help in this process and do believe that our manuscript has been improved as a result of your comments.  Please see our responses below.

 

Reviewer 4:

The manuscript is devoted to the development and evaluation of a specific Landsat albedo product. Generally, the research satisfies the requirements for publications however, the authors need to consider the following questions.

1. The title is too broad and confusing

We have clarified that we are using Landsat 8 albedo data to narrow the field of focus.

2. The section materials and methods are not concentrated on the exact methods and data that have been used.

Thank you for this insight, we have expanded the methodology to include a more expansive and specific description of the method.

3. Fig 1 is too small, no idea that it could be obtained from that map. 

We appreciate feedback, we have made the figure larger however it is supposed to be a generalized overview of data used for validation with the absolute coordinates presented in Table 1.

4. Table 1 is too long and can be sent in the appendix. 

Thank you for this feedback, while it is long, we feel it is very relevant to the text and provides a great deal of contextual information.  If the editors would like us to move it to the appendix, however, we are very willing to do so.

This research needs to clarify the situation with permafrost that covers a major part of the region and has big uncertainties with a contribution to albedo. I found only "Tundra Vegetation".  What about other types of permafrost? 

The product does produce albedo across the entire region including over non-vegetated areas as well as snow- and ice-covered surfaces.  Many of the high latitude towers included in this validation effort are within the permafrost zone and included in this effort.  The albedo-permafrost feedback loop is an important component of climate change modelling and hopefully this product can be used in future efforts to evaluate this connection.  We have added a sentence to that effect in the introduction.

 

Author Response File: Author Response.docx

Reviewer 5 Report

The proposed manuscript evaluated a 30m Landsat operational blue-sky albedo product at the circumpolar region by using high-quality ground measurements. Overall, the manuscript is well written, the results are very promising, and it provides a detailed statement and discussion regarding the algorithm and uncertainty analysis. I suggest a major revision before it can be accepted.

 

1. Figure 3: suggest providing some explanations regarding the scattered samples in (a), samples with large SZA can be marked by different symbols, and validation statistics should be included in the figure.

 

2. Figure 4: can you provide some explanation why several AERONET-derived albedo values are missed compared to MODIS AOD-derived results?

 

3. Figure 5: the validation statistics need to be included in the figure as Figure 3.

 

4. Figure 6: Considering that this article specifically focuses on the circumpolar region and snow cover will introduce significant heterogeneity based on previous results, readers would be interested in the performance of the Landsat albedo when the image has snow covered compared to MODIS. Suggest including a similar analysis by adding an example in the snow season.

 

Abstract, Discussion, and Conclusion: These sections didn't follow a general format of academic articles. The background intro in the Abstract takes too much proportion, suggest using 1-3 sentences to do the intro, 1 sentence to clarify the issue to be dealt with, 1-2 sentences to introduce your method and work, 1-2 sentences to summarize the results and contributions, and the last sentence to point out the broad impact of the study. The Discussion provides a lot of background knowledge that should be mentioned in the Introduction, suggest simplifying this section and mainly explaining the uncertainty and limitation of the proposed results. In the Conclusion, the basic results should be summarized.

 

Minor:

Table 1: a title is needed, and the contents in columns of Sill2.0 and R @ 2km need to be explained in the context.

Line 316: the accuracy standard should have a citation.

Is it possible to attach the data availability information of the operational Landsat albedo product?

Author Response

Dear reviewer,

 

Thank you for spending so much time reviewing this work and for your thoughtful and considered comments.  We have done our best to address the issues highlighted.   We appreciate your help in this process and do believe that our manuscript has been improved as a result of your comments.  Please see our responses below.

 

Reviewer 5 comments:

The proposed manuscript evaluated a 30m Landsat operational blue-sky albedo product at the circumpolar region by using high-quality ground measurements. Overall, the manuscript is well written, the results are very promising, and it provides a detailed statement and discussion regarding the algorithm and uncertainty analysis. I suggest a major revision before it can be accepted.

1. Figure 3: suggest providing some explanations regarding the scattered samples in (a), samples with large SZA can be marked by different symbols, and validation statistics should be included in the figure.

            Statistics have been added, thank you. We have noted snow and snow-free data points with different symbols because the data presented here is already restricted to less that SZA of less than 70 degrees.  We have also added some text regarding the scatter of the data in the figure caption. 

2. Figure 4: can you provide some explanation why several AERONET-derived albedo values are missed compared to MODIS AOD-derived results?

We only used Level 2.0 data which is cloud cleared and calibrated. While AERONET also provides additional product levels, they do so with the disclaimer that the data can change in future data releases. Text to this effect has been added to the caption of Figure 4.

3. Figure 5: the validation statistics need to be included in the figure as Figure 3.

            Statistics have been added, thank you,

4. Figure 6: Considering that this article specifically focuses on the circumpolar region and snow cover will introduce significant heterogeneity based on previous results, readers would be interested in the performance of the Landsat albedo when the image has snow covered compared to MODIS. Suggest including a similar analysis by adding an example in the snow season.

            Thank you for this suggestion, we have added additional analysis to Figure 6.

Abstract, Discussion, and Conclusion: These sections didn't follow a general format of academic articles. The background intro in the Abstract takes too much proportion, suggest using 1-3 sentences to do the intro, 1 sentence to clarify the issue to be dealt with, 1-2 sentences to introduce your method and work, 1-2 sentences to summarize the results and contributions, and the last sentence to point out the broad impact of the study. The Discussion provides a lot of background knowledge that should be mentioned in the Introduction, suggest simplifying this section and mainly explaining the uncertainty and limitation of the proposed results. In the Conclusion, the basic results should be summarized.

We appreciate this observation and have taken some time to rework the text to better conform with this structure.

 

Minor:

Table 1: a title is needed, and the contents in columns of Sill2.0 and R @ 2km need to be explained in the context.

            Title has been added and text amended to improve the description of the data presented.

Line 316: the accuracy standard should have a citation.

A reference has been added, thank you.

Is it possible to attach the data availability information of the operational Landsat albedo product?

            We are finalizing the data delivery to the LPDAAC and will update when implemented

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 5 Report

The revision and feedback are sounding and I would suggest accepting this manuscript.